Field of the Invention
The present invention relates to a vibration wave motor, and more particularly, to a vibration wave motor for linear drive including a plate-like elastic body. The present invention also relates to a driving apparatus using the vibration wave motor and to a driving apparatus including the vibration wave motor described above.
Description of the Related Art
Hitherto, vibration wave motors with features of small-size and lightweight, high-speed drive, and quiet drive have been employed for lens barrels of image pickup apparatus. Among the vibration wave motors, the following vibration wave motor is described in Japanese Patent Application Laid-Open No. 2012-16107 as a vibration wave motor for linear drive.
FIG. 20A to FIG. 20G are diagrams for illustrating a configuration of a related-art vibration wave motor 600. FIG. 20A is a plan view, FIG. 20B is a front view, FIG. 20C and FIG. 20D are side views, and FIG. 20E is a bottom view. In FIG. 20A to FIG. 20G, a vibrating plate 601 has a rectangular surface. On the rectangular surfaces of the vibrating plate 601, two projections 601a and 601b are provided.
A piezoelectric device 602 having a rectangular shape that vibrates at high frequency is bonded to the surface of the vibrating plate 601 on a side opposite to the surface where the projections 601a and 601b are provided. The piezoelectric device 602 includes two regions obtained by polarization in the same direction, that is, regions 602a and 602b. The region 602a is allocated to an A-phase, whereas the region 602b is allocated to a B-phase. An unpolarized region 602c serves as an electrode to be used as a ground that is conductive to a full-scale electrode on a back surface 602d of the piezoelectric device 602 through a side surface.
Further, coupling portions 601c and 601d to be directly or indirectly coupled to a vibrator holding member (not shown) move in synchronization with the vibrating plate 601. The coupling portions 601c and 601d are provided to shorter sides D2 of the rectangular surface of the vibrating plate 601. As described above, the vibrating plate 601 and the piezoelectric device 602 form the vibrating wave motor 600.
In FIG. 20E, an illustration is made of a node and antinodes of torsional vibration in a secondary natural vibration mode in a direction of longer sides D1 under a state in which the vibrating plate 601, the piezoelectric device 602, and the projections 601a and 601b are integrated. In FIG. 20E, a node and antinodes of bending vibration in a primary natural vibration mode in a direction of the shorter sides D2 are illustrated. Further, FIG. 20F is an illustration of the bending vibration in a secondary natural vibration mode in the direction of the longer sides D1 as viewed in a direction indicated by the arrow d1. FIG. 20G is an illustration of the bending vibration in the primary natural vibration mode in the direction of the shorter sides D2 as viewed in a direction indicated by the arrow d2. In FIG. 20F and FIG. 20G, the illustration of the projections 601a and 601b, the coupling portions 601c and 601d, and the piezoelectric device 602 is omitted.
In FIG. 20E, the antinode of the bending vibration in the primary natural vibration mode in the direction of the shorter sides D2 is indicated by X, whereas the nodes of the bending vibration in the secondary natural vibration mode in the direction of the longer sides D1 are indicated by Y1 and Y2. The projections 601a and 601b are formed in the vicinity of the antinode (indicated by X) of the bending vibration in the primary natural vibration mode in the direction of the shorter sides D2 as well as in the vicinity of the nodes (indicated by Y1 and Y2) of the bending vibration in the secondary natural vibration mode in the direction of the longer sides D1. Further, by applying AC voltages from a power feeding unit (not shown) with a phase difference between the A-phase and the B-phase being freely changed, the vibration with vibration waves can be caused.
FIG. 21A to FIG. 21D are illustrations of a state of the vibration when the AC voltages are applied with the B-phase being delayed by about +90° with respect to the A-phase. FIG. 21A is a graph of changes in the AC voltages applied to the A-phase and the B-phase of the piezoelectric device. FIG. 21B, FIG. 21C, and FIG. 21D correspond to FIG. 20B, FIG. 20C, and FIG. 20D, and are illustrations of changes in vibration with time from P1′ to P4′.
Further, in FIG. 21A, the illustration of the piezoelectric device 602 and the coupling portions 601c and 601d is omitted. With respect to electric changes P1 to P4 in the AC voltage shown in FIG. 21A, the mechanical changes P1′ to P4′ in vibration illustrated in FIG. 21B, FIG. 21C, and FIG. 21D have a predetermined mechanical response delay time. Further, an amplitude of the vibration is illustrated in an exaggerated manner. The details of the driving principle and speed control of the vibration wave motor 600 are described in Japanese Patent Application Laid-Open No. 2012-16107.
In recent years, there is a growing need of downsizing electronic equipment in which the vibration wave motor is mounted, in particular, a lens driving apparatus. As described below, however, the related-art vibration wave motor has a limitation to downsize the apparatus.
First, a configuration of a linear driving apparatus using the related-art vibration wave motor is described. FIG. 22A and FIG. 22B are schematic diagrams of a linear driving apparatus 700 using the related-art vibration wave motor. FIG. 22A is a diagram as viewed in a movement direction of the vibration wave motor, and FIG. 22B is a sectional view taken along the line 22B-22B of FIG. 22A. As illustrated in FIG. 22A and FIG. 22B, the vibration wave motor includes the vibrating plate 601 and the piezoelectric device 602. Further, the vibration wave motor further includes a friction member 701 fixed to a frame body (not shown) with which the projections 601a and 601b come into contact for frictional driving, and rollers 702 provided on a back surface of the friction member 701 so as to rotationally slide thereon.
The vibration wave motor further supports the vibrating plate 601 by the coupling portions 601c and 601d, and further includes a holding member 703 for holding a vibrator that connects the rollers 702. The vibration wave motor further includes a pressure spring 704 and a drive transmitting portion 705. The pressure spring 704 has an upper end acting on the holding member 703 and a lower end acting on the piezoelectric device 602. The drive transmitting portion 705 is configured to be coupled with a driven body. By a pressurizing force of the pressure spring 704, the projections 601a and 601b are brought into pressure-contact with the friction member 701, and obtain a thrust force in the X-direction illustrated in FIG. 22B by a driving force generated by circular motion indicated by the arrows B illustrated in FIG. 22B.
Next, a configuration of the lens driving apparatus in which the linear driving apparatus using the related-art vibration wave motor is mounted is described. FIG. 23A to FIG. 23C are schematic views of a lens driving portion. FIG. 23A is a front view in an optical axis direction, and FIG. 23B and FIG. 23C are side views in which a frame body is partially broken away. FIG. 23C is an illustration of a lens driving apparatus that is further downsized as compared with that illustrated in FIG. 23B. In FIG. 23A to FIG. 23C, the lens driving apparatus includes a frame body 801, a lens 802, a lens holder 803, and guiding shafts 804 and 805 that support the lens holder 803 and guide the lens holder 803 in the optical axis direction (in the X-direction in FIG. 23B). In FIG. 23B, the illustration of the components other than the vibrating plate 601 and the friction member 701 is omitted from the linear driving apparatus 700. In accordance with a motion instruction issued from a microcomputer (not shown), the linear driving apparatus 700 moves over a corresponding distance. As a result, the lens holder 803 can be moved within a range from a left position indicated by the solid line in FIG. 23B to a right position 803′ indicated by the broken line.
As described above, a range occupied by the vibrating plate 601, which becomes an obstacle in downsizing of the linear driving apparatus and the lens driving apparatus, is the sum of a motion distance L1 of the lens holder 803 and a size L2 of the vibrating plate 601 in the movement direction. Therefore, for the downsizing of the whole lens driving apparatus illustrated in FIG. 23B, the size L2 of the vibrating plate 601 in the movement direction needs to be reduced. In the lens driving apparatus that is downsized as illustrated in FIG. 23C, the achievement of reduction of the size L2 of the vibrating plate 601 in the movement direction becomes more important for the downsizing of the whole apparatus.
However, the related-art vibration wave motor has a configuration that is elongated in the movement direction, as illustrated in FIG. 20A to FIG. 20G. Therefore, the reduction of the size L2 in the movement direction has the following problem. If the whole apparatus is similarly reduced in size so as to simply reduce a total length, an area of the piezoelectric device becomes smaller to reduce deformation caused by a piezoelectric effect. Thus, a vibrational amplitude is reduced. Further, the entire size of the combination of the piezoelectric device and the vibrating plate is reduced to increase a resonant frequency. Thus, the vibrational amplitude is reduced.
As a result, the amplitude in the movement direction indicated by (ii) in FIG. 21A to FIG. 21D is reduced. Therefore, it is predicted that the thrust force is lowered. Further, as a result of reduction of the amplitude in a perpendicular direction indicated by (i) in FIG. 21A to FIG. 21D, the amplitude in the perpendicular direction (i) is insufficient for a surface roughness of a slider. Thus, it is also predicted that there arises a problem in that the thrust force cannot be obtained. Therefore, the reduction of the size L2 in the movement direction in the related-art vibration wave motor has a limit.
As described above, the size of the vibration wave motor in the movement direction needs to be reduced to downsize the driving apparatus. With the configuration of the related-art vibration wave motor, however, it is difficult to reduce the size of the vibration wave motor in the movement direction without losing the thrust force.